Conventionally, an indicating instrument for vehicles includes a dial plate having a plurality of display portions; light sources for luminously displaying the dial plate; movements for extending their pointer shafts forward of the dial plate; control circuits for driving the movements so that the pointer shafts are rotated by angles according to individual measured values detected by external detectors or the like and also for controlling ON and OFF of the light sources; and a printed circuit board. The printed circuit board is disposed backward of the dial plate to constitute an electric circuit by accommodating the light sources, the movements, and the control circuits. For example, this is described in JP-2003-75206-A (U.S. 2003/0043048 A1).
In the above instrument, the respective light sources or movements are formed on the printed circuit board in correspondence to positions of the display portions, i.e., indicators that indicate existence/nonexistence of abnormality and operating states of parts of the vehicle; gauges for various instruments. Further, the control circuits are appropriately disposed in free spaces other than spaces for the light sources and the movements.
The light sources include light emitting diodes (LEDs), while the movements include a cross-coil type actuator or a stepping motor.
The movement is driven by applying voltage in pulse to it. Also, the LEDs are controlled in their lighting by applying the voltage in pulse to them. This varies a duty of ON/OFF, enabling easy control of lighting intensity.
Namely, a control circuit generates the voltage in pulse, so that so-called electrical noise is radiated and potentially adversely affects other electric devices mounted on the vehicle, e.g., a radio receiver, a phone.
The electrical noise level from the printed circuit board varies depending on wiring patterns thereof, i.e., positions of the LEDs, movements, and control circuits. Therefore, the positions of the LEDs, movements, and control circuits are adjusted so that the radiated noise can be decreased to a harmless level.
Further, when the above indicating instrument is mounted on a different vehicle type, or when the display portions of the dial panel are changed by the design change due to a model change of a vehicle or the like, the LEDs and the movements simultaneously need changing in their layouts.
As a result, in response to installation in a different vehicle type, or to a model change of a vehicle, work cycles are repeated to decrease the electrical noise to the harmless level each time the printed circuit is re-designed. The work cycle includes circuit designing, prototype manufacturing, evaluating, design improving, etc., which entails a lot of man power.